Global motion constrained motion vector in inter prediction

ABSTRACT

A decoder includes circuitry configured to receive a bitstream, extract a header associated with a current frame and including a signal characterizing that global motion is enabled and further characterizing parameters of a global motion model, and decoding the current frame, the decoding including using a motion model for each current block having a complexity that is less than or equal to a complexity of the global motion model. Related apparatus, systems, techniques, and articles are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of InternationalApplication No. PCT/US 20/29926, filed on Apr. 24, 2020 and entitled“GLOBAL MOTION CONSTRAINED MOTION VECTOR IN INTER PREDICTION,” whichclaims the benefit of priority of U.S. Provisional Patent ApplicationSer. No. 63/838,563, filed on Apr. 25, 2019, and titled “GLOBAL MOTIONCONSTRAINED MOTION VECTOR IN INTER PREDICTION.” Each of InternationalApplication No. PCT/US 20/29926 and U.S. Provisional Patent ApplicationSer. No. 63/838,563 is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of videocompression. In particular, the present invention is directed to globalmotion constrained motion vector in inter prediction.

BACKGROUND

A video codec can include an electronic circuit or software thatcompresses or decompresses digital video. It can convert uncompressedvideo to a compressed format or vice versa. In the context of videocompression, a device that compresses video (and/or performs somefunction thereof) can typically be called an encoder, and a device thatdecompresses video (and/or performs some function thereof) can be calleda decoder.

A format of the compressed data can conform to a standard videocompression specification. The compression can be lossy in that thecompressed video lacks some information present in the original video. Aconsequence of this can include that decompressed video can have lowerquality than the original uncompressed video because there isinsufficient information to accurately reconstruct the original video.

There can be complex relationships between the video quality, the amountof data used to represent the video (e.g., determined by the bit rate),the complexity of the encoding and decoding algorithms, sensitivity todata losses and errors, ease of editing, random access, end-to-end delay(e.g., latency), and the like.

Motion compensation can include an approach to predict a video frame ora portion thereof given a reference frame, such as previous and/orfuture frames, by accounting for motion of the camera and/or objects inthe video. It can be employed in the encoding and decoding of video datafor video compression, for example in the encoding and decoding usingthe Motion Picture Experts Group (MPEG)-2 (also referred to as advancedvideo coding (AVC) and H.264) standard. Motion compensation can describea picture in terms of the transformation of a reference picture to thecurrent picture. The reference picture can be previous in time whencompared to the current picture, from the future when compared to thecurrent picture. When images can be accurately synthesized frompreviously transmitted and/or stored images, compression efficiency canbe improved.

SUMMARY OF THE DISCLOSURE

In an aspect, a decoder includes circuitry configured to receive abitstream, extract a header associated with a current frame andincluding a signal characterizing that global motion is enabled andfurther characterizing parameters of a global motion model, and decodethe current frame, the decoding including using a motion model for eachcurrent block having a complexity that is less than or equal to acomplexity of the global motion model.

In another aspect, a method includes receiving, by a decoder, abitstream. The method includes extracting a header associated with acurrent frame and including a signal characterizing that global motionis enabled and further characterizing parameters of a motion model. Themethod includes decoding the current frame, the decoding including usinga motion model for each current block having a complexity that is lessthan or equal to a complexity of the global motion model.

These and other aspects and features of non-limiting embodiments of thepresent invention will become apparent to those skilled in the art uponreview of the following description of specific non-limiting embodimentsof the invention in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a diagram illustrating motion vectors of an example frame withglobal and local motion;

FIG. 2 illustrates three example motion models that can be utilized forglobal motion including their index value (0, 1, or 2);

FIG. 3 is a process flow diagram according to some exampleimplementations of the current subject matter;

FIG. 4 is a system block diagram of an example decoder according to someexample implementations of the current subject matter;

FIG. 5 is a process flow diagram according to some exampleimplementations of the current subject matter;

FIG. 6 is a system block diagram of an example encoder according to someexample implementations of the current subject matter; and

FIG. 7 is a block diagram of a computing system that can be used toimplement any one or more of the methodologies disclosed herein and anyone or more portions thereof.

The drawings are not necessarily to scale and may be illustrated byphantom lines, diagrammatic representations and fragmentary views. Incertain instances, details that are not necessary for an understandingof the embodiments or that render other details difficult to perceivemay have been omitted.

DETAILED DESCRIPTION

“Global motion” in video refers to motion and/or a motion model commonto all pixels of a region, where a region may be a picture, a frame, orany portion of a picture or frame such as a block, CTU, or other subsetof contiguous pixels. Global motion may be caused by camera motion; forexample, camera panning and zooming may create motion in a frame thatmay typically affect the entire frame. Motion present in portions of avideo may be referred to as local motion. Local motion may be caused bymoving objects in a scene, such as without limitation an object movingfrom left to right in the scene. Videos may contain a combination oflocal and global motion. Some implementations of the current subjectmatter may provide for efficient approaches to communicate global motionto a decoder and use of global motion vectors in improving compressionefficiency.

FIG. 1 is a diagram illustrating motion vectors of an example frame 100with global and local motion. Frame 100 includes a number of blocks ofpixels illustrated for exemplary purposes as squares, and theirassociated motion vectors illustrated as arrows. Squares (e.g., blocksof pixels) with arrows pointing up and to the left indicate blocks withmotion that may be considered to be global motion and squares witharrows pointing in other directions (indicated by 104) may indicateblocks with local motion. In the illustrated example of FIG. 1, manyblocks have same global motion. Signaling global motion in a header,such as a picture parameter set (PPS) or sequence parameter set (SPS)and using signaled global motion may reduce motion vector informationneeded by blocks and may result in improved prediction. Although forillustrative purposes examples described below refer to determinationand/or application of global or local motion vectors at a block level,global motion vectors may be determined and/or applied for any region ofa frame and/or picture, including regions made up of multiple blocks,regions bounded by any geometric form such as without limitation regionsdefined by geometric and/or exponential coding in which one or morelines and/or curves bounding the shape may be angled and/or curved,and/or an entirety of a frame and/or picture. Although signaling isdescribed herein as being performed at a frame level and/or in a headerand/or parameter set of a frame, signaling may alternatively oradditionally be performed at a sub-picture level, where a sub-picturemay include any region of a frame and/or picture as described above.

As an example, and still referring to FIG. 1, simple translationalmotion may be described using a motion vector (MV) with two componentsMVx, MVy that describes displacement of blocks and/or pixels in acurrent frame. More complex motion such as rotation, zooming, andwarping may be described using affine motion vectors, where an “affinemotion vector,” as used in this disclosure, is a vector describing auniform displacement of a set of pixels or points represented in a videopicture and/or picture, such as a set of pixels illustrating an objectmoving across a view in a video without changing apparent shape duringmotion. Some approaches to video encoding and/or decoding may use4-parameter or 6-parameter affine models for motion compensation ininter picture coding.

For example, a six-parameter affine motion can be described as:

x′=ax+by+c

y′=dx+ey+f

A four-parameter affine motion can be described as:

x′=ax+by+c

y′=−bx+ay+f

where (x,y) and (x′,y′) are pixel locations in current and referencepictures, respectively; a, b, c, d, e, and f are parameters of an affinemotion model.

Still referring to FIG. 1, parameters used to describe affine motion maybe signaled to a decoder to apply affine motion compensation at thedecoder. In some approaches, motion parameters may be signaledexplicitly or by signaling translational control point motion vectors(CPMVs) and then deriving affine motion parameters from thetranslational control point motion vectors. Two control point motionvectors (CPMVs) may be utilized to derive affine motion parameters for afour-parameter affine motion model and three control point translationalmotion vectors (CPMVs) may be utilized to obtain parameters for asix-parameter motion model. Signaling affine motion parameters usingcontrol point motion vectors may allow use of efficient motion vectorcoding methods to signal affine motion parameters.

In some implementations, and continuing to refer to FIG. 1, globalmotion signaling may be included in a header, such as a PPS or SPS.Global motion may vary from picture to picture. Motion vectors signaledin picture headers may describe motion relative to previously decodedframes. In some implementations, global motion may be translational oraffine. Motion model (e.g., number of parameters, whether the model isaffine, translational, or other) used may also be signaled in a pictureheader. FIG. 2 illustrates three example motion models 200 that may beutilized for global motion including their index value (0, 1, or 2).

Still referring to FIG. 2, PPSs may be used to signal parameters thatcan change between pictures of a sequence. Parameters that remain thesame for a sequence of pictures may be signaled in a sequence parameterset to reduce a size of PPS and reduce video bitrate. An example pictureparameter set (PPS) is shown in table 1:

Descriptor pic_parameter_set_rbsp( ) { pps_pic_parameter_set_id ue(v)pps_seq_parameter_set_id u(4) mixed_nalu_types_in_pic_flag u(1)pic_width_in_luma_samples ue(v) pic_height_in_luma_samples ue(v)pps_conformance_window_flag u(1) if( pps_conformance_window_flag ) {pps_conf_win_left_offset ue(v) pps_conf_win_right_offset ue(v)pps_conf_win_top_offset ue(v) pps_conf_win_bottom_offset ue(v) }scaling_window_explicit_signalling_flag u(1) if(scaling_window_explicit_signalling_flag ) { scaling_win_left_offsetue(v) scaling_win_right_offset ue(v) scaling_win_top_offset ue(v)scaling_win_bottom_offset ue(v) } output_flag_present_flag u(1)subpic_id_mapping_in_pps_flag u(1) if( subpic_id_mapping_in_pps_flag ) {pps_num_subpics_minus1 ue(v) pps_subpic_id_len_minus1 ue(v) for( i = 0;i <= pps_num_subpic_minus1; i++ ) pps_subpic_id[ i ] u(v) }no_pic_partition_flag u(1) if( !no_pic_partition_flag ) {pps_log2_ctu_size_minus5 u(2) num_exp_tile_columns_minus1 ue(v)num_exp_tile_rows_minus1 ue(v) for( i = 0; i <=num_exp_tile_columns_minus1; i++ ) tile_column_width_minus1[ i ] ue(v)for( i = 0; i <= num_exp_tile_rows_minus1; i++ ) tile_row_height_minus1[i ] ue(v) if( NumTilesInPic > 1 ) rect_slice_flag u(1) if(rect_slice_flag ) single_slice_per_subpic_flag u(1) if( rect_slice_flag&& !single_slice_per_subpic_flag ) { num_slices_in_pic_minus1 ue(v) if(num_slices_in_pic_minus1 > 0 ) tile_idx_delta_present_flag u(1) for( i =0; i < num_slices_in_pic_minus1; i++ ) { if( NumTileColumns > 1 )slice_width_in_tiles_minus1[ i ] ue(v) if( NumTileRows > 1 && (tile_idx_delta_present_flag | | SliceTopLeftTileIdx[ i ] %NumTileColumns = = 0 ) ) slice_height_in_tiles_minus1[ i ] ue(v) if(slice_width_in_tiles_minus1[ i ] = = 0 && slice_height_in_tiles_minus1[i ] = = 0 && RowHeight[ SliceTopLeftTileIdx[ i ] / NumTileColumns ] > 1) { num_exp_slices_in_tile[ i ] ue(v) for( j = 0; j <num_exp_slices_in_tile[ i ]; j++ ) exp_slice_height_in_ctus_minus1[ i ][j ] ue(v) i += NumSlicesInTile[ i ] − 1 } if(tile_idx_delta_present_flag && i < num_slices_in_pic_minus1 )tile_idx_delta[ i ] se(v) } } loop_filter_across_tiles_enabled_flag u(1)loop_filter_across_slices_enabled_flag u(1) } cabac_init_present_flagu(1) for( i = 0; i < 2; i++ ) num_ref_idx_default_active_minus1[ i ]ue(v) rpl1_idx_present_flag u(1) init_qp_minus26 se(v)cu_qp_delta_enabled_flag u(1) pps_chroma_tool_offsets_present_flag u(1)if( pps_chroma_tool_offsets_present_flag ) { pps_cb_qp_offset se(v)pps_cr_qp_offset se(v) pps_joint_cbcr_qp_offset_present_flag u(1) if(pps_joint_cbcr_qp_offset_present_flag ) pps_joint_cbcr_qp_offset_valuese(v) pps_slice_chroma_qp_offsets_present_flag u(1)pps_cu_chroma_qp_offset_list_enabled_flag u(1) } if(pps_cu_chroma_qp_offset_list_enabled_flag ) {chroma_qp_offset_list_len_minus1 ue(v) for( i = 0; i <=chroma_qp_offset_list_len_minus1; i++ ) { cb_qp_offset_list[ i ] se(v)cr_qp_offset_list[ i ] se(v) if( pps_joint_cbcr_qp_offset_present_flag )joint_cbcr_qp_offset_list[ i ] se(v) } } pps_weighted_pred_flag u(1)pps_weighted_bipred_flag u(1) deblocking_filter_control_present_flagu(1) if( deblocking_filter_control_present_flag ) {deblocking_filter_override_enabled_flag u(1)pps_deblocking_filter_disabled_flag u(1) if(!pps_deblocking_filter_disabled_flag ) { pps_beta_offset_div2 se(v)pps_tc_offset_div2 se(v) pps_cb_beta_offset_div2 se(v)pps_cb_tc_offset_div2 se(v) pps_cr_beta_offset_div2 se(v)pps_cr_tc_offset_div2 se(v) } } rpl_info_in_ph_flag u(1) if(deblocking_filter_override_enabled_flag ) dbf_info_in_ph_flag u(1)sao_info_in_ph_flag u(1) alf_info_in_ph_flag u(1) if( (pps_weighted_pred_flag | | pps_weighted_bipred_flag ) &&rpl_info_in_ph_flag ) wp_info_in_ph_flag u(1) qp_delta_info_in_ph_flagu(1) pps_ref_wraparound_enabled_flag u(1) if(pps_ref_wraparound_enabled_flag ) pps_ref_wraparound_offset ue(v)picture_header_extension_present_flag u(1)slice_header_extension_present_flag u(1) pps_extension_flag u(1) if(pps_extension_flag) while( more_rbsp_data( ) ) pps_extension_data_flagu(1) rbsp_trailing_bits( ) }

Additional fields may be added to the PPS to signal global motion. Incase of global motion, presence of global motion parameters in asequence of pictures may be signaled in a SPS and a PPS may referencethe SPS by SPS ID. SPS in some approaches to decoding may be modified toadd a field to signal presence of global motion parameters in SPS. Forexample, a one-bit field may be added to the SPS. Ifglobal_motion_present bit is 1, global motion related parameters may beexpected in a PPS. If global_motion_present bit is 0, no global motionparameter related fields may be present in PPS. For example, the PPS oftable 1 may be extended to include a global_motion_present field, forexample, as shown in table 2:

Descriptor sequence_parameter_set_rbsp( ) {sps_sequence_parameter_set_id ue(v) . . global_motion_present u(1)rbsp_trailing_bits( ) }

Similarly, the PPS can include a pps global motion parameters field fora frame, for example as shown in table 3:

Descriptor pic_parameter_set_rbsp( ) { pps_pic_parameter_set_id ue(v)pps_seq_parameter_set_id ue(v) . . . pps_global_motion_parameters ( )rbsp_trailing_bits( ) }

In more detail, a PPS may include fields to characterize global motionparameters using control point motion vectors, for example as shown intable 4:

Descriptor pps_global_motion_parameters ( ) { motion_model_used u(2)mv0_x se(v) mv1_y se(v) if(motion_model_used == 1){ mv1_x se(v) mv1_yse(v) } if(motion_model_used == 2){ mv2_x se(v) mv2_y se(v) } }

As a further non-limiting example, Table 5 below may represent anexemplary SPS:

Descriptor seq_parameter_set_rbsp( ) { sps_seq_parameter_set_id u(4)sps_video_parameter_set_id u(4) sps_max_sublayers_minus1 u(3)sps_reserved_zero_4bits u(4) sps_ptl_dpb_hrd_params_present_flag u(1)if( sps_ptl_dpb_hrd_params_present_flag ) profile_tier_level( 1,sps_max_sublayers_minus1 ) gdr_enabled_flag u(1) chroma_format_idc u(2)if( chroma_format_idc = = 3 ) separate_colour_plane_flag u(1)res_change_in_clvs_allowed_flag u(1) pic_width_max_in_luma_samples ue(v)pic_height_max_in_luma_samples ue(v) sps_conformance_window_flag u(1)if( sps_conformance_window_flag ) { sps_conf_win_left_offset ue(v)sps_conf_win_right_offset ue(v) sps_conf_win_top_offset ue(v)sps_conf_win_bottom_offset ue(v) } sps_log2_ctu_size_minus5 u(2)subpic_info_present_flag u(1) if( subpic_info_present_flag ) {sps_num_subpics_minus1 ue(v) sps_independent_subpics_flag u(1) for( i =0; sps_num_subpics_minus1 > 0 && i <= sps_num_subpics_minus1; i++) { if(i > 0 && pic_width_max_in_luma_samples > CtbSizeY )subpic_ctu_top_left_x[ i ] u(v) if( i > 0 &&pic_height_max_in_luma_samples > CtbSizeY ) { subpic_ctu_top_left_y[ i ]u(v) if( i < sps_num_subpics_minus1 && pic_width_max_in_luma_samples >CtbSizeY ) subpic_width_minus1[ i ] u(v) if( i < sps_num_subpics_minus1&& pic_height_max_in_luma_samples > CtbSizeY ) subpic_height_minus1[ i ]u(v) if( !sps_independent_subpics_flag ) { subpic_treated_as_pic_flag[ i] u(1) loop_filter_across_subpic_enabled_flag[ i ] u(1) } }sps_subpic_id_len_minus1 ue(v)subpic_id_mapping_explicitly_signalled_flag u(1) if(subpic_id_mapping_explicitly_signalled_flag ) {subpic_id_mapping_in_sps_flag u(1) if( subpic_id_mapping_in_sps_flag )for( i = 0; i <= sps_num_subpics_minus1; i++ ) sps_subpic_id[ i ] u(v) }} bit_depth_minus8 ue(v) sps_entropy_coding_sync_enabled_flag u(1) if(sps_entropy_coding_sync_enabled_flag )sps_wpp_entry_point_offsets_present_flag u(1) sps_weighted_pred_flagu(1) sps_weighted_bipred_flag u(1) log2_max_pic_order_cnt_lsb_minus4u(4) sps_poc_msb_flag u(1) if( sps_poc_msb_flag ) poc_msb_len_minus1ue(v) num_extra_ph_bits_bytes u(2) extra_ph_bits_struct(num_extra_ph_bits_bytes ) num_extra_sh_bits_bytes u(2)extra_sh_bits_struct( num_extra_sh_bits_bytes ) if(sps_max_sublayers_minus1 > 0 ) sps_sublayer_dpb_params_flag u(1) if(sps_ptl_dpb_hrd_params_present_flag ) dpb_parameters(sps_max_sublayers_minus1, sps_sublayer_dpb_params_flag )long_term_ref_pics_flag u(1) inter_layer_ref_pics_present_flag u(1)sps_idr_rpl_present_flag u(1) rpl1_same_as_rpl0_flag u(1) for( i = 0; i< rpl1_same_as_rpl0_flag ? 1 : 2; i++ ) { num_ref_pic_lists_in_sps[ i ]ue(v) for( j = 0; j < num_ref_pic_lists_in_sps[ i ]; j++ )ref_pic_list_struct( i, j ) } if( ChromaArrayType != 0 )qtbtt_dual_tree_intra_flag u(1) log2_min_luma_coding_block_size_minus2ue(v) partition_constraints_override_enabled_flag u(1)sps_log2_diff_min_qt_min_cb_intra_slice_luma ue(v)sps_max_mtt_hierarchy_depth_intra_slice_luma ue(v) if(sps_max_mtt_hierarchy_depth_intra_slice_luma != 0 ) {sps_log2_diff_max_bt_min_qt_intra_slice_luma ue(v)sps_log2_diff_max_tt_min_qt_intra_slice_luma ue(v) }sps_log2_diff_min_qt_min_cb_inter_slice ue(v)sps_max_mtt_hierarchy_depth_inter_slice ue(v) if(sps_max_mtt_hierarchy_depth_inter_slice != 0 ) {sps_log2_diff_max_bt_min_qt_inter_slice ue(v)sps_log2_diff_max_tt_min_qt_inter_slice ue(v) } if(qtbtt_dual_tree_intra_flag ) {sps_log2_diff_min_qt_min_cb_intra_slice_chroma ue(v)sps_max_mtt_hierarchy_depth_intra_slice_chroma ue(v) if(sps_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) {sps_log2_diff_max_bt_min_qt_intra_slice_chroma ue(v)sps_log2_diff_max_tt_min_qt_intra_slice_chroma ue(v) } }sps_max_luma_transform_size_64_flag u(1) if( ChromaArrayType != 0 ) {sps_joint_cbcr_enabled_flag u(1) same_qp_table_for_chroma u(1)numQpTables = same_qp_table_for_chroma ? 1 : (sps_joint_cbcr_enabled_flag ? 3 : 2 ) for( i = 0; i < numQpTables; i++ ){ qp_table_start_minus26[ i ] se(v) num_points_in_qp_table_minus1[ i ]ue(v) for( j = 0; j <= num_points_in_qp_table_minus1[ i ]; j++ ) {delta_qp_in_val_minus1[ i ][ j ] ue(v) delta_qp_diff_val[ i ][ j ] ue(v)} } } sps_sao_enabled_flag u(1) sps_alf_enabled_flag u(1) if(sps_alf_enabled_flag && ChromaArrayType != 0 ) sps_ccalf_enabled_flagu(1) sps_transform_skip_enabled_flag u(1) if(sps_transform_skip_enabled_flag ) { log2_transform_skip_max_size_minus2ue(v) sps_bdpcm_enabled_flag u(1) } sps_ref_wraparound_enabled_flag u(1)sps_temporal_mvp_enabled_flag u(1) if( sps_temporal_mvp_enabled_flag )sps_sbtmvp_enabled_flag u(1) sps_amvr_enabled_flag u(1)sps_bdof_enabled_flag u(1) if( sps_bdof_enabled_flag )sps_bdof_pic_present_flag u(1) sps_smvd_enabled_flag u(1)sps_dmvr_enabled_flag u(1) if( sps_dmvr_enabled_flag )sps_dmvr_pic_present_flag u(1) sps_mmvd_enabled_flag u(1)sps_isp_enabled_flag u(1) sps_mrl_enabled_flag u(1) sps_mip_enabled_flagu(1) if( ChromaArrayType != 0 ) sps_cclm_enabled_flag u(1) if(chroma_format_idc = = 1 ) { sps_chroma_horizontal_collocated_flag u(1)sps_chroma_vertical_collocated_flag u(1) } sps_mts_enabled_flag u(1) if(sps_mts_enabled_flag ) { sps_explicit_mts_intra_enabled_flag u(1)sps_explicit_mts_inter_enabled_flag u(1) } six_minus_max_num_merge_candue(v) sps_sbt_enabled_flag u(1) sps_affine_enabled_flag u(1) if(sps_affine_enabled_flag ) { five_minus_max_num_subblock_merge_cand ue(v)sps_affine_type_flag u(1) if( sps_amvr_enabled_flag )sps_affine_amvr_enabled_flag u(1) sps_affine_prof_enabled_flag u(1) if(sps_affine_prof_enabled_flag ) sps_prof_pic_present_flag u(1) }sps_palette_enabled_flag u(1) if( ChromaArrayType = = 3 &&!sps_max_luma_transform_size_64_flag ) sps_act_enabled_flag u(1) if(sps_transform_skip_enabled_flag | | sps_palette_enabled_flag )min_qp_prime_ts_minus4 ue(v) sps_bcw_enabled_flag u(1)sps_ibc_enabled_flag u(1) if( sps_ibc_enabled_flag )six_minus_max_num_ibc_merge_cand ue(v) sps_ciip_enabled_flag u(1) if(sps_mmvd_enabled_flag) sps_fpel_mmvd_enabled_flag u(1) if(MaxNumMergeCand >= 2 ) { sps_gpm_enabled_flag u(1) if(sps_gpm_enabled_flag && MaxNumMergeCand >= 3 )max_num_merge_cand_minus_max_num_gpm_cand ue(v) } sps_lmcs_enabled_flagu(1) sps_lfnst_enabled_flag u(1) sps_ladf_enabled_flag u(1) if(sps_ladf_enabled_flag ) { sps_num_ladf_intervals_minus2 u(2)sps_ladf_lowest_interval_qp_offset se(v) for( i = 0; i <sps_num_ladf_intervals_minus2 + 1; i++ ) { sps_ladf_qp_offset[ i ] se(v)sps_ladf_delta_threshold_minus1[ i ] ue(v) } }log2_parallel_merge_level_minus2 ue(v)sps_explicit_scaling_list_enabled_flag u(1) sps_dep_quant_enabled_flagu(1) if( !sps_dep_quant_enabled_flag ) sps_sign_data_hiding_enabled_flagu(1) sps_virtual_boundaries_enabled_flag u(1) if(sps_virtual_boundaries_enabled_flag ) {sps_virtual_boundaries_present_flag u(1) if(sps_virtual_boundaries_present_flag ) { sps_num_ver_virtual_boundariesu(2) for( i = 0; i < sps_num_ver_virtual_boundaries; i++ )sps_virtual_boundaries_pos_x[ i ] u(13) sps_num_hor_virtual_boundariesu(2) for( i = 0; i < sps_num_hor_virtual_boundaries; i++ )sps_virtual_boundaries_pos_y[ i ] u(13) } } if(sps_ptl_dpb_hrd_params_present_flag ) {sps_general_hrd_params_present_flag u(1) if(sps_general_hrd_params_present_flag ) { general_hrd_parameters( ) if(sps_max_sublayers_minus1 > 0 ) sps_sublayer_cpb_params_present_flag u(1)firstSubLayer = sps_sublayer_cpb_params_present_flag ? 0 :sps_max_sublayers_minus1 ols_hrd_parameters( firstSubLayer,sps_max_sublayers_minus1 ) } } field_seq_flag u(1)vui_parameters_present_flag u(1) if( vui_parameters_present_flag )vui_parameters( ) /* Specified in ITU-T H.SEI|ISO/IEC 23002-7 */sps_extension_flag u(1) if( sps_extension_flag ) while( more_rbsp_data() ) sps_extension_data_flag u(1) rbsp_trailing_bits( ) }

An SPS table as above may be expanded as described above to incorporatea global motion present indicator as shown in Table 6:

Descriptor sequence_parameter_set_rbsp( ) {sps_sequence_parameter_set_id ue(v) . . . global_motion_present u(1)rbsp_trailing_bits( ) }

Additional fields may be incorporated in an SPS to reflect furtherindicators as described in this disclosure.

In an embodiment, and still referring to FIG. 2, ansps_affine_enabled_flag in a PPS and/or SPS may specify whether affinemodel based motion compensation may be used for inter prediction. Ifsps_affine_enabled_flag is equal to 0, the syntax may be constrainedsuch that no affine model based motion compensation is used in the codelater video sequence (CLVS), and inter_affine_flag andcu_affine_type_flag may not be present in coding unit syntax of theCLVS. Otherwise (sps_affine_enabled_flag is equal to 1), affine modelbased motion compensation can be used in the CLVS.

Continuing to refer to FIG. 2, sps_affine_type_flag in a PPS and/or SPSmay specify whether 6-parameter affine model based motion compensationmay be used for inter prediction. If sps_affine_type_flag is equal to 0,syntax may be constrained such that no 6-parameter affine model basedmotion compensation is used in the CLVS, and cu_affine_type_flag may notpresent in coding unit syntax in the CLVS. Otherwise(sps_affine_type_flag_equal to 1), 6-parameter affine model based motioncompensation may be used in CLVS. When not present, the value ofsps_affine_type_flag may be inferred to be equal to 0.

Further referring to FIG. 2, sps_6param_affine_enabled_flag_equal to 1may specify that the 6-parameter affine model based motion compensationis enabled for the CLVS.

Still referring to FIG. 2, translational CPMVs may be signaled in PPS.Control points may be predefined. For example, control point MV 0 may berelative to a top left corner of a picture, MV 1 may be relative to atop right corner, and MV 3 may be relative to a bottom left corner ofthe picture. Table 4 illustrates an example approach for signaling CPMVdata depending on a motion model used.

In an exemplary embodiment, and still referring to FIG. 2, an arrayamvr_precision_idx, which may be signaled in coding unit, coding tree,or the like, may specify a resolution AmvrShift of a motion vectordifference, which may be defined as a non-limiting example as shown inTable 7 as shown below. Array indices x0, y0 may specify the location(x0, y0) of a top-left luma sample of a considered coding block relativeto a top-left luma sample of the picture; whenamvr_precision_idx[x0][y0] is not present, it may be inferred to beequal to 0. Where an inter_affine_flag[x0][y0] is equal to 0, variablesMvdL0[x0][y0][0], MvdL0[x0][y0][1], MvdL1[x0][y0][0], MvdL1[x0][y0][1]representing modsion vector difference values corresponding to conseredblock, may be modified by shifting such values by AmvrShift, forinstance using MvdL0[x0][y0][0]=MvdL0[x0][y0][0]<<AmvrShift;MvdL0[x0][y0][1]=MvdL0[x0][y0][1]<<AmvrShift;MvdL1[x0][y0][0]=MvdL1[x0][y0][0]<<AmvrShift; andMvdL1[x0][y0][1]=MvdL1[x0][y0][1]<<AmvrShift. Whereinter_affine_flag[x0][y0] is equal to 1, variablesMvdCpL0[x0][y0][0][0], MvdCpL0[x0][y0][0][1], MvdCpL0[x0][y0][1][0],MvdCpL0[x0][y0][1][1], MvdCpL0[x0][y0][2][0] and MvdCpL0[x0][y0][2][1]may be modified via shifting, for instance as follows:MvdCpL0[x0][y0][0][0]=MvdCpL0[x0][y0][0][0]<<AmvrShift; MvdCpL1[x0][y0][0][1]=MvdCpL1[x0][y0][0][1]<<AmvrShift;MvdCpL0[x0][y0][1][0]=MvdCpL0[x0][y0][1][0]<<AmvrShift; MvdCpL1[x0][y0][1][1]=MvdCpL1[x0][y0][1][1]<<AmvrShift;MvdCpL0[x0][y0][2][0]=MvdCpL0[x0][y0][2][0]<<AmvrShift; andMvdCpL1[x0][y0] [2][1]=MvdCpL1[x0][y0][2][1]<<AmvrShift

AmvrShift inter_af- amvr_preci- inter_af- CuPredMode[ chType ][ x0 ][ y0] = = fine_flag = =0&&CuPredMode[ chType ][ x0 ][ y0 ] != amvr_flagsion_i fine_flag = =1 MODE_IBC ) MODE_IBC 0 — 2 (¼ luma sample) — 2 (¼luma sample) 1 0 0 ( 1/16 luma sample) 4 (1 luma sample) 3 (½ lumasample) 1 1 4 (1 luma sample) 6 (4 luma samples) 4 (1 luma sample) 1 2 —— 6 (4 luma samples)

Further referring to FIG. 2, global motion may be relative to apreviously coded frame. When only one set of global motion parametersare present, motion may be relative to a frame that is presentedimmediately before a current frame.

Still referring to FIG. 2, global motion may represent a dominant motionin a frame. Many blocks in a frame may be likely to have a motion thatis same as very similar to a global motion. Exceptions may be blockswith local motion. Keeping block motion compensation compatible withglobal motion may reduce encoder complexity and decoder complexity andmay improve compression efficiency.

In some implementations, and continuing to refer to FIG. 2, if globalmotion is signaled in a header such as a PPS or an SPS, a motion modelin the SPS may be applied to all blocks in a picture. For example, ifglobal motion uses translational motion (e.g., motion model=0), allprediction units (PUs) in a frame may also be limited to translationalmotion (e.g., motion model=0). In this case, adaptive motion models maynot be used. This may also be signaled in SPS using ause_gm_constrained_motion_models flag. When this flag is set to 1,adaptive motion models may not be used in a decoder; instead, a singlemotion model may be used for all PUs.

Still referring to FIG. 2, in some implementations of the currentsubject matter, motion signaling may not change over PUs. Instead, afixed motion model may be used by signaling a motion model once in SPS.Such an approach may replace global motion. Use of fixed motion modelmay be specified at an encoder to reduce complexity; for instance, theencoder may be limited to translational model, which can be advantageousfor low power devices, such as low computational power devices. Forexample, affine motion models may not be used, for instance as specifiedin an encoder profile. Such an example may be useful for real-timeapplications, such as video conferencing, information of things (IoT)infrastructure, security cameras, and the like. By using a fixed motionmodel, there may be no need to include excess signaling in thebitstream.

Further referring to FIG. 2, the current subject matter is not limitedto coding techniques utilizing global motion but may apply to a broadrange of coding techniques.

As described above, and still referring to FIG. 2, global motion mayrepresent a dominant motion in a frame. Many blocks in a frame may belikely to have a motion that is same as very similar to global motion,with exception of blocks with local motion. Keeping block motioncompensation compatible with global motion may reduce encoder complexityand decoder complexity, and may improve compression efficiency.

Still referring to FIG. 2, rather than constraining the motion of eachblock to be the same as a motion model, such as without limitation aglobal motion model, signaled in a header, such as a PPS or an SPS,motion model applied to each block in a frame may be constrained tosimilar motion models. Similar motion models may include those modelsthat have the same complexity or are less complex. For example, thefollowing three models are shown in the first column of table 5 inincreasing order of complexity.

Global Motion Model Motion Model Use in Inter Coding Translational (MM =0) Translational 4-parameter affine (MM = 1) Translational or4-parameter affine 6-parameter affine (MM = 2) Translational or4-parameter affine or 6-parameter affine

Still referring to FIG. 2, the second column of table 5 showspermissible motion models for a block to use for inter coding. Forexample, some implementations of the current subject matter may allow aPU to take on a motion model where an index of the motion model is lessthan or equal to an index of the motion model for global motion.

With continued reference to FIG. 2, keeping motion models compatiblewith global motion may allow for use of global motion control points asmotion vector prediction candidates. Global motion CPMVs may representmotion similar to motion of PUs and make good MV prediction candidates.

FIG. 3 is a process flow diagram illustrating an exemplary embodiment ofa process 300 of the applying a similar motion model to a global motionmodel signaled in a header.

At step 305, a bitstream is received by a decoder. A current block maybe contained within a bitstream that a decoder receives. Bitstream mayinclude, for example, data found in a stream of bits that is an input toa decoder when using data compression. Bitstream may include informationnecessary to decode a video. Receiving may include extracting and/orparsing a block and associated signaling information from bit stream. Insome implementations, a current block may include a coding tree unit(CTU), a coding unit (CU), and/or a prediction unit (PU).

At step 310, and still referring to FIG. 3, a header associated with acurrent frame and including a signal characterizing that global motionis enabled and further characterizing parameters of a motion model canbe extracted. At step 315, a current frame may be decoded. Decoding mayinclude using a motion model for each current block having a complexitythat is less than or equal to a complexity of a global motion model.

FIG. 4 is a system block diagram illustrating an exemplary embodiment ofa decoder 2400 capable of decoding a bitstream including applying asimilar motion model to a global motion model signaled in a header.Decoder 400 may include an entropy decoder processor 404, an inversequantization and inverse transformation processor 408, a deblockingfilter 412, a frame buffer 416, a motion compensation processor 420and/or an intra prediction processor 424.

In operation, and still referring to FIG. 4, bit stream 428 may bereceived by decoder 400 and input to entropy decoder processor 404,which may entropy decode portions of bit stream into quantizedcoefficients. Quantized coefficients may be provided to inversequantization and inverse transformation processor 408, which may performinverse quantization and inverse transformation to create a residualsignal, which may be added to an output of motion compensation processor420 or intra prediction processor 424 according to a processing mode. Anoutput of the motion compensation processor 420 and intra predictionprocessor 424 may include a block prediction based on a previouslydecoded block. A sum of prediction and residual may be processed bydeblocking filter 412 and stored in a frame buffer 416.

FIG. 3 is a process flow diagram illustrating an exemplary embodiment ofa process 300 of encoding a video including applying a similar motionmodel to a global motion model signaled in a header according to someaspects of the current subject matter that may reduce encodingcomplexity while increasing compression efficiency. At step 305, a videoframe may undergo initial block segmentation, for example, using atree-structured macro block partitioning scheme that may includepartitioning a picture frame into CTUs and CUs.

At step 310, and still referring to FIG. 3, a global motion for acurrent block or frame may be determined. At step 315, block may beencoded and included in bitstream. Encoding may include signaling in aheader that for all blocks in a frame, a similar motion model to aglobal motion model should be applied. Encoding may include utilizinginter prediction and intra prediction modes, for example.

FIG. 6 is a system block diagram illustrating an exemplary embodiment ofa video encoder 600 capable of applying a similar motion model to aglobal motion model signaled in a header. Example video encoder 600 mayreceive an input video 604, which may be initially segmented and/ordividing according to a processing scheme, such as a tree-structuredmacro block partitioning scheme (e.g., quad-tree plus binary tree). Anexample of a tree-structured macro block partitioning scheme may includepartitioning a picture frame into large block elements called codingtree units (CTU). In some implementations, each CTU may be furtherpartitioned one or more times into a number of sub-blocks called codingunits (CU). A final result of this portioning may include a group ofsub-blocks that may be called predictive units (PU). Transform units(TU) may also be utilized.

Still referring to FIG. 6, example video encoder 600 may include anintra prediction processor 612, a motion estimation/compensationprocessor 612 (also referred to as an inter prediction processor)capable of constructing a motion vector candidate list including addinga single global motion vector candidate to the motion vector candidatelist, a transform/quantization processor 616, an inversequantization/inverse transform processor 620, an in-loop filter 624, adecoded picture buffer 628, and/or an entropy coding processor 632. Bitstream parameters may be input to entropy coding processor 632 forinclusion in an output bit stream 636.

In operation, and with continued reference to FIG. 6, for each block ofa frame of input video 604, whether to process block via intra pictureprediction or using motion estimation/compensation may be determined.Block may be provided to intra prediction processor 608 or motionestimation/compensation processor 612. If block is to be processed viaintra prediction, intra prediction processor 608 may perform processingto output a predictor. If block is to be processed via motionestimation/compensation, motion estimation/compensation processor 612may perform processing including constructing a motion vector candidatelist including adding a single global motion vector candidate to themotion vector candidate list, if applicable.

Still referring to FIG. 6, a residual may be formed by subtractingpredictor from input video. Residual may be received bytransform/quantization processor 616, which may perform transformationprocessing (e.g., discrete cosine transform (DCT)) to producecoefficients, which may be quantized. Quantized coefficients and anyassociated signaling information may be provided to entropy codingprocessor 632 for entropy encoding and inclusion in an output bit stream636. Entropy encoding processor 632 may support encoding of signalinginformation related to encoding a current block. In addition, quantizedcoefficients may be provided to inverse quantization/inversetransformation processor 620, which may reproduce pixels, which may becombined with predictor and processed by in loop filter 624, an outputof which may be stored in decoded picture buffer 628 for use by motionestimation/compensation processor 612 that is capable of constructing amotion vector candidate list including adding a single global motionvector candidate to the motion vector candidate list.

Further referencing FIG. 6, although a few variations have beendescribed in detail above, other modifications or additions arepossible. For example, in some implementations, current blocks mayinclude any symmetric blocks (8×8, 16×16, 32×32, 64×64, 128×128, and thelike) as well as any asymmetric block (8×4, 16×8, and the like).

In some implementations, and still referring to FIG. 6, a quadtree plusbinary decision tree (QTBT) may be implemented. In QTBT, at a CodingTree Unit level, partition parameters of QTBT may be dynamically derivedto adapt to local characteristics without transmitting any overhead.Subsequently, at a Coding Unit level, a joint-classifier decision treestructure may eliminate unnecessary iterations and control risk of falseprediction. In some implementations, LTR frame block update mode may beavailable as an additional option available at every leaf node of aQTBT.

In some implementations, and still referring to FIG. 6, additionalsyntax elements may be signaled at different hierarchy levels of abitstream. For example, a flag may be enabled for an entire sequence byincluding an enable flag coded in a Sequence Parameter Set (SPS).Further, a CTU flag may be coded at a coding tree unit (CTU) level.

It is to be noted that any one or more of the aspects and embodimentsdescribed herein may be conveniently implemented using digitalelectronic circuitry, integrated circuitry, specially designedapplication specific integrated circuits (ASICs), field programmablegate arrays (FPGAs) computer hardware, firmware, software, and/orcombinations thereof, as realized and/or implemented in one or moremachines (e.g., one or more computing devices that are utilized as auser computing device for an electronic document, one or more serverdevices, such as a document server, etc.) programmed according to theteachings of the present specification, as will be apparent to those ofordinary skill in the computer art. These various aspects or featuresmay include implementation in one or more computer programs and/orsoftware that are executable and/or interpretable on a programmablesystem including at least one programmable processor, which may bespecial or general purpose, coupled to receive data and instructionsfrom, and to transmit data and instructions to, a storage system, atleast one input device, and at least one output device. Appropriatesoftware coding may readily be prepared by skilled programmers based onthe teachings of the present disclosure, as will be apparent to those ofordinary skill in the software art. Aspects and implementationsdiscussed above employing software and/or software modules may alsoinclude appropriate hardware for assisting in the implementation of themachine executable instructions of the software and/or software module.

Such software may be a computer program product that employs amachine-readable storage medium. A machine-readable storage medium maybe any medium that is capable of storing and/or encoding a sequence ofinstructions for execution by a machine (e.g., a computing device) andthat causes the machine to perform any one of the methodologies and/orembodiments described herein. Examples of a machine-readable storagemedium include, but are not limited to, a magnetic disk, an optical disc(e.g., CD, CD-R, DVD, DVD-R, etc.), a magneto-optical disk, a read-onlymemory “ROM” device, a random access memory “RAM” device, a magneticcard, an optical card, a solid-state memory device, an EPROM, an EEPROM,Programmable Logic Devices (PLDs), and/or any combinations thereof. Amachine-readable medium, as used herein, is intended to include a singlemedium as well as a collection of physically separate media, such as,for example, a collection of compact discs or one or more hard diskdrives in combination with a computer memory. As used herein, amachine-readable storage medium does not include transitory forms ofsignal transmission.

Such software may also include information (e.g., data) carried as adata signal on a data carrier, such as a carrier wave. For example,machine-executable information may be included as a data-carrying signalembodied in a data carrier in which the signal encodes a sequence ofinstruction, or portion thereof, for execution by a machine (e.g., acomputing device) and any related information (e.g., data structures anddata) that causes the machine to perform any one of the methodologiesand/or embodiments described herein.

Examples of a computing device include, but are not limited to, anelectronic book reading device, a computer workstation, a terminalcomputer, a server computer, a handheld device (e.g., a tablet computer,a smartphone, etc.), a web appliance, a network router, a networkswitch, a network bridge, any machine capable of executing a sequence ofinstructions that specify an action to be taken by that machine, and anycombinations thereof. In one example, a computing device may includeand/or be included in a kiosk.

FIG. 7 shows a diagrammatic representation of one embodiment of acomputing device in the exemplary form of a computer system 700 withinwhich a set of instructions for causing a control system to perform anyone or more of the aspects and/or methodologies of the presentdisclosure may be executed. It is also contemplated that multiplecomputing devices may be utilized to implement a specially configuredset of instructions for causing one or more of the devices to performany one or more of the aspects and/or methodologies of the presentdisclosure. Computer system 700 includes a processor 704 and a memory708 that communicate with each other, and with other components, via abus 712. Bus 712 may include any of several types of bus structuresincluding, but not limited to, a memory bus, a memory controller, aperipheral bus, a local bus, and any combinations thereof, using any ofa variety of bus architectures.

Memory 708 may include various components (e.g., machine-readable media)including, but not limited to, a random-access memory component, a readonly component, and any combinations thereof. In one example, a basicinput/output system 716 (BIOS), including basic routines that help totransfer information between elements within computer system 700, suchas during start-up, may be stored in memory 708. Memory 708 may alsoinclude (e.g., stored on one or more machine-readable media)instructions (e.g., software) 720 embodying any one or more of theaspects and/or methodologies of the present disclosure. In anotherexample, memory 708 may further include any number of program modulesincluding, but not limited to, an operating system, one or moreapplication programs, other program modules, program data, and anycombinations thereof.

Computer system 700 may also include a storage device 724. Examples of astorage device (e.g., storage device 724) include, but are not limitedto, a hard disk drive, a magnetic disk drive, an optical disc drive incombination with an optical medium, a solid-state memory device, and anycombinations thereof. Storage device 724 may be connected to bus 712 byan appropriate interface (not shown). Example interfaces include, butare not limited to, SCSI, advanced technology attachment (ATA), serialATA, universal serial bus (USB), IEEE 1394 (FIREWIRE), and anycombinations thereof. In one example, storage device 724 (or one or morecomponents thereof) may be removably interfaced with computer system 700(e.g., via an external port connector (not shown)). Particularly,storage device 724 and an associated machine-readable medium 728 mayprovide nonvolatile and/or volatile storage of machine-readableinstructions, data structures, program modules, and/or other data forcomputer system 700. In one example, software 720 may reside, completelyor partially, within machine-readable medium 728. In another example,software 720 may reside, completely or partially, within processor 704.

Computer system 700 may also include an input device 732. In oneexample, a user of computer system 700 may enter commands and/or otherinformation into computer system 700 via input device 732. Examples ofan input device 732 include, but are not limited to, an alpha-numericinput device (e.g., a keyboard), a pointing device, a joystick, agamepad, an audio input device (e.g., a microphone, a voice responsesystem, etc.), a cursor control device (e.g., a mouse), a touchpad, anoptical scanner, a video capture device (e.g., a still camera, a videocamera), a touchscreen, and any combinations thereof. Input device 732may be interfaced to bus 712 via any of a variety of interfaces (notshown) including, but not limited to, a serial interface, a parallelinterface, a game port, a USB interface, a FIREWIRE interface, a directinterface to bus 712, and any combinations thereof. Input device 732 mayinclude a touch screen interface that may be a part of or separate fromdisplay 736, discussed further below. Input device 732 may be utilizedas a user selection device for selecting one or more graphicalrepresentations in a graphical interface as described above.

A user may also input commands and/or other information to computersystem 700 via storage device 724 (e.g., a removable disk drive, a flashdrive, etc.) and/or network interface device 740. A network interfacedevice, such as network interface device 740, may be utilized forconnecting computer system 700 to one or more of a variety of networks,such as network 744, and one or more remote devices 748 connectedthereto. Examples of a network interface device include, but are notlimited to, a network interface card (e.g., a mobile network interfacecard, a LAN card), a modem, and any combination thereof. Examples of anetwork include, but are not limited to, a wide area network (e.g., theInternet, an enterprise network), a local area network (e.g., a networkassociated with an office, a building, a campus or other relativelysmall geographic space), a telephone network, a data network associatedwith a telephone/voice provider (e.g., a mobile communications providerdata and/or voice network), a direct connection between two computingdevices, and any combinations thereof. A network, such as network 744,may employ a wired and/or a wireless mode of communication. In general,any network topology may be used. Information (e.g., data, software 720,etc.) may be communicated to and/or from computer system 700 via networkinterface device 740.

Computer system 700 may further include a video display adapter 752 forcommunicating a displayable image to a display device, such as displaydevice 736. Examples of a display device include, but are not limitedto, a liquid crystal display (LCD), a cathode ray tube (CRT), a plasmadisplay, a light emitting diode (LED) display, and any combinationsthereof. Display adapter 752 and display device 736 may be utilized incombination with processor 704 to provide graphical representations ofaspects of the present disclosure. In addition to a display device,computer system 700 may include one or more other peripheral outputdevices including, but not limited to, an audio speaker, a printer, andany combinations thereof. Such peripheral output devices may beconnected to bus 712 via a peripheral interface 756. Examples of aperipheral interface include, but are not limited to, a serial port, aUSB connection, a FIREWIRE connection, a parallel connection, and anycombinations thereof.

The foregoing has been a detailed description of illustrativeembodiments of the invention. Various modifications and additions can bemade without departing from the spirit and scope of this invention.Features of each of the various embodiments described above may becombined with features of other described embodiments as appropriate inorder to provide a multiplicity of feature combinations in associatednew embodiments. Furthermore, while the foregoing describes a number ofseparate embodiments, what has been described herein is merelyillustrative of the application of the principles of the presentinvention. Additionally, although particular methods herein may beillustrated and/or described as being performed in a specific order, theordering is highly variable within ordinary skill to achieve embodimentsas disclosed herein. Accordingly, this description is meant to be takenonly by way of example, and not to otherwise limit the scope of thisinvention.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it is used, such a phrase isintended to mean any of the listed elements or features individually orany of the recited elements or features in combination with any of theother recited elements or features. For example, the phrases “at leastone of A and B;” “one or more of A and B;” and “A and/or B” are eachintended to mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” In addition, use of the term “based on,” aboveand in the claims is intended to mean, “based at least in part on,” suchthat an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and sub-combinations of the disclosed featuresand/or combinations and sub-combinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. A decoder, the decoder comprising circuitryconfigured to: receive a bitstream; extract a header associated with acurrent frame and including a signal characterizing that global motionis enabled and further characterizing parameters of a global motionmodel; and decode the current frame, the decoding including using amotion model for each current block having a complexity that is lessthan or equal to a complexity of the global motion model.
 2. The decoderof claim 1, wherein the motion model includes translational motion. 3.The decoder of claim 1, wherein the motion model includes affine motion.4. The decoder of claim 1, wherein the header includes a pictureparameter set (PPS).
 5. The decoder of claim 1, wherein the headerincludes a sequence parameter set (SPS).
 6. The decoder of claim 1,wherein the motion model includes a translational motion model.
 7. Thedecoder of claim 1, wherein the motion model includes a four-parameteraffine motion model.
 8. The decoder of claim 1, wherein the motion modelincludes a six-parameter affine motion model.
 9. The decoder of claim 1,wherein each current block is a coding tree unit
 10. The decoder ofclaim 1, wherein each current block is a coding unit
 11. A methodcomprising: receiving, by a decoder, a bitstream; extracting a headerassociated with a current frame and including a signal characterizingthat global motion is enabled and further characterizing parameters of amotion model; and decoding the current frame, the decoding includingusing a motion model for each current block having a complexity that isless than or equal to a complexity of the global motion model.
 12. Themethod of claim 11, wherein the motion model includes translationalmotion
 13. The method of claim 11, wherein the motion model includesaffine motion.
 14. The method of claim 11, wherein the header includes apicture parameter set (PPS).
 15. The method of claim 11, wherein theheader includes a sequence parameter set (SPS).
 16. The method of claim11, wherein the motion model includes a translational motion model. 17.The method of claim 11, wherein the motion model includes afour-parameter affine motion model.
 18. The method of claim 11, whereinthe motion model includes a six-parameter affine motion model.
 19. Themethod of claim 11, wherein each current block is a coding tree unit.20. The method of claim 11, wherein each current block is a coding unit.